The present invention relates to a microwave plasma treatment apparatus for subjecting objects of treatment, such as semiconductor wafers, to etching and other specific treatments with plasmas formed by using microwaves.
An ECR (electron cyclotron resonance) etching apparatus, as an example of a microwave plasma treatment apparatus, comprises a treatment chamber (etching chamber) and a plasma generating chamber. Set in the treatment chamber is a stage of, for example, stainless steel, which can carry thereon an object of treatment, such as a semiconductor wafer or LCD or glass substrate. The plasma generating chamber is connected with a waveguide that serves to propagate microwaves, generated by means of a magnetron of a microwave generator, to the plasma generating chamber.
In the ECR etching apparatus constructed in this manner, a specific treatment gas is introduced into the treatment chamber, and TE11-mode microwaves (e.g., at 2.45 GHz), for example, are introduced into the a plasma generating chamber through the waveguide and an insulating wall. In the plasma generating chamber, a plasma is generated by microwave discharge, and reaction gases in the treatment gas are dissociated to produce radicals by the agency of the plasma. The plasma and radicals are guided to the stage that carries the object of treatment thereon, whereupon a to-be-treated film on the object is etched with them.
As compared with a conventional parallel-plate plasma treatment apparatus, the microwave plasma treatment apparatus of this type, having the following features, is better suited for highly fine working that is demanded these days.
[Features of Microwave Plasma Treatment Apparatus]
(1) Shape control can be effected with ease, covering varieties of etching from anisotropic etching to perfectly isotropic etching.
(2) The ionization ratio is high enough to ensure high-speed etching with lower ion energy that is less damaging.
(3) No-electrode discharge in a treatment chamber of, for example, quartz enables etching with fewer sources of pollution.
FIG. 5A is a sectional view of a waveguide 10 taken along a plane perpendicular to the direction of propagation of microwaves (axial direction of the waveguide 10), in which are described electric- and magnetic-field vectors of TE11-mode microwaves (electromagnetic waves) propagated through the waveguide 10. TE waves (transverse electric waves) are electromagnetic waves whose electric-field vectors are always directed at right angles to the direction of propagation thereof. The TE11-mode microwaves, in particular, are electromagnetic waves whose electric- and magnetic-field vectors are directed at right angles to one another and also to the advancing direction of the waves, as shown in FIG. 5A, and which are propagated in the circular waveguide, a path of propagation proper to them.
As is generally known, electric lines of force extend at right angles to an equipotential surface. Accordingly, the electric lines of force of microwaves that are propagated through a waveguide extend at right angles to the inner surface of the waveguide. In the case where an inner surface 10a of the waveguide 10 is formed having a circular cross section perpendicular to the axis of the waveguide, in order to propagate the TE11-mode microwaves, therefore, those electric lines of force which do not pass the central portion of the waveguide 10 have high curvatures, as shown in FIG. 5A. More specifically, the curvatures (degrees of inward bend) of the electric lines of force become higher with distance from the central portion of the waveguide 10, in the direction of a magnetic line of force (magnetic-field direction), and lower with distance from the peripheral portion. Thus, the density of the electric lines of force becomes lower with distance from the central portion of the waveguide 10 in the direction of the magnetic line of force and higher with distance from the peripheral portion. In consequence, the electric-field intensity (P) of the microwaves becomes lower with distance from the central portion of the waveguide 10 in the direction of the magnetic line and higher with distance from the peripheral portion, as shown in FIG. 5B (electric-field intensity distribution of the microwaves in the direction of the magnetic line of force).
The electric-field intensity distribution of the microwaves is reflected in the density of plasmas excited in the plasma generating chamber. If it is uneven, as shown in FIG. 5B, the plasma density distribution also becomes uneven, so that the object of treatment may possibly fail to be subjected to a uniform plasma treatment.
The object of the present invention is to provide a microwave plasma treatment apparatus capable of subjecting an object of treatment to a uniform plasma treatment by using TE11-mode microwaves.
The above object of the invention is achieved by a microwave plasma treatment apparatus constructed as follows. The apparatus comprises microwave generating means for generating TE11-mode microwaves, a circular waveguide for propagating the TE11-mode microwaves generated from the microwave generating means, plasma generating means for generating a plasma by using the TE11-mode microwaves propagated through the circular waveguide, and a treatment chamber for treating an object of treatment with the plasma generated by the plasma generating means. Those inner surface regions of the circular waveguide which are opposed to each other in the electric-field direction of the microwaves are deformed so that the electric-field intensity of the microwaves introduced in TE11-mode is substantially uniform in the magnetic-field direction of the microwaves.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.